1. Field of the Invention
The present invention relates to a temperature-controlled fan fluid coupling which controls the rotation of a fan for cooling an automobile engine to supply an adequate amount of cooling air to the engine always according to the operating conditions and, more particularly, to an improvement over the fan fluid coupling already proposed by the present applicant in Japanese Patent Publication No. 7846/1984.
2. Description of the Prior Art
A conventional fan fluid coupling of this kind is shown in FIG. 9, where an enclosed housing is formed by a cover 23' and a case 23". The inside of this housing is divided into an oil reservoir chamber 25 and a torque transmission chamber 26 by a partition plate 24 that is provided with a hole 24' for controlling the outflow of oil. A driving disk 22 is mounted inside the torque transmission chamber 26. A circulatory passage 27 which is in communication with the working portion extends from the torque transmission chamber 26 into the oil reservoir chamber 25. A dam 28 is formed in the passage 27 which has an entrance port 27' and an exit port 27". A substantially hemispherical groove 29 is in communication with the passage 27 which is formed by retaining a partition wall on the inner surface of the oil reservoir chamber 25. The exit port 27" is located at the front open end of the groove 29 to place at least one of the entrance port 27' and the exit port 27" above the level of the oil existing in the oil reservoir chamber 25 whenever the engine stops.
In the conventional fan fluid coupling, when the engine stops or is at idle, the passage 27 is immersed in the oil held in the oil reservoir chamber 25. The oil is prevented from spontaneously flowing back into the torque transmission chamber 26 from the oil reservoir chamber through the passage 27. Therefore, the oil is prevented from being collected in the torque transmission chamber. Immediately after the engine is restarted, the rotational speed of the fan is prevented from increasing rapidly. This keeps the fan from producing extraordinarily loud noise. Also, in cold weather the warm-up of the engine is effectively performed. When the engine is at a high temperature, a valve member opens the outflow-adjusting hole 24' formed in the partition plate 24. Under this condition, if the engine is stopped while this hole 24' is immersed in the oil in the oil reservoir chamber 25, then the oil spontaneously flows out of the oil reservoir chamber through the hole 24', so that a large amount of oil is collected in the torque transmission chamber 26. Consequently, after the engine is restarted, the rotational speed of the driven fan increases for a given time as indicated by the performance characteristic line C in FIG. 10. This phenomenon is called drag.
When the engine is restarted as described above, if the valve member still opens the outflow-adjusting hole 24', then supply of oil into the torque transmission chamber 26 through the hole 24' is continued. As a result, the driven fan is maintained at a high rotational speed as indicated by the line C'. When the engine is restarted, if the valve member closes the hole 24', the fast rotation is maintained as indicated by the line C" until oil flows out of the torque transmission chamber via the dam.